Brochure

Gas-to-Flare Control Valve
All gas processing facilities have a are system to safeguard against
overpressure of critical assets within the plant and dispose of
any waste gas. Failure of the are system to successfully relieve
pressure from the process can lead to unexpected downtime or
damage to costly pressure-retaining equipment.
Gas-to-are valves are installed at numerous locations throughout
the gas treatment and liquefaction units to control the ow of
feed gas or refrigerant to the are stack for disposal. They are
primarily used during plant startup, shutdown, or short-duration
upset conditions. During these periods, are valves will experience
signicant pressure differentials and high ow rates. If not
addressed properly, these conditions can lead to excessive noise
levels and even damaging vibration.
Emerson utilizes the industry standard for aerodynamic noise
modeling and prediction in control valves, IEC 60534-8-3. This
standard models two independent sources of noise -- the valve
trim and the valve body outlet. In applications with moderate
pressure drop, noise attenuating trim is commonly sufcient to
maintain overall noise levels at acceptable levels. However, in
high pressure drop applications such as gas-to-are, the valve
body outlet noise will commonly overcome the trim noise as the
dominant source. To account for this, Emerson’s engineers use the
latest IEC noise prediction model to account for both independent
sources of noise when developing custom valve solutions for your
high pressure drop applications. This comprehensive approach
incorporates noise-attenuating technology to reduce trim noise
and a properly-sized valve body outlet to maintain acceptable
noise levels at the outlet.
During the normal operation of the plant, gas-to-are valves will
remain closed. Because of this, it is important that these valves
maintain tight, long-term shutoff in order to prevent loss of
valuable product to the are stack.
A gas processing plant in Saudi Arabia
experienced cracking of a NPS 54 acid
flare header made of Inconel. Two
Emerson engineers studied the process
conditions and concluded that the
existing valves were contributing to
excessive vibration and noise. Despite the
use of noise-attenuating trim, the valves
had not been properly sized to account for valve body outlet noise,
which resulted in valve outlet velocities close to sonic – 0.7 mach.
After several visits to this remote site, Emerson recommended a larger
replacement valve with Fisher WhisperFlo
™
trim that would meet all of
the process conditions.
Existing valves were replaced by two NPS 16 Fisher ET control valves
with WhisperFlo Level Z trim. The valves lowered the velocity of the
outlet to 0.3 mach, which significantly reduced the noise at the valve
and the vibration affecting the downstream piping.
A Case-In-Point
Scan this code or visit
www.FisherSevereService.com
to learn about the science of noise
attenuation in control valves and
our history of solving noise issues in
facilities just like yours.
14 | Fisher
®
LNG Liquefaction Solutions